This disclosure is directed to a high pressure high temperature detonator system particularly adapted to be used in a perforating gun assembly. In drilling a deep well in seeking petroleum reserves, the well often becomes so deep that it is exposed to extremely high pressures and temperatures. The ambient temperature can be as high as 500.degree. F. and the pressure can be as high as 25,000 psi. Generally, the conditions become more severe as the well becomes deeper. As deeper and deeper wells are drilled, the prevailing conditions are so severe that safe detonation becomes a problem.
A perforating gun is typically an elongate tubular body which supports one or more shaped charges. The carrier which supports the shaped charges typically must include a type of detonator, detonator cord, and connections to several shaped charges. Normally, this assembly is lowered into a well by means of an electric wireline. Sometimes, it can be lowered into a well on a tubing string. The perforating gun assembly is lowered to the required depth. It is fired by providing an electric current to the detonator ignitor which starts detonation along the detonating cord. Alternatively, a dropped weight may trigger firing in a tubing conveyed perforating gun assembly. In either case, it is necessary for the detonation to proceed along the detonating cord to all the shaped charges for detonation in sequence. There are usually many shaped charges in such as assembly. While it is possible to have only a single charge, they are normally connected in series somewhat in the fashion of a series of Christmas tree lights. In similar fashion, they all must operate to assure proper detonation.
In the event the detonating cord fails at some mid point of an assembly supporting N shaped charges, then the first several shaped charges may properly detonate, but the remaining shaped charges will not. This divides the N shaped charges in the two groups, those which are properly detonated and those which do not detonate as a result of failure. This creates a very dangerous condition for retrieval of the assembly. Namely, it is dangerous because there are live shaped charges remaining in the assembly when it is pulled out of the well. They can possibly detonate at the wrong elevation, and even worse, they can detonate at the top of the well, risking injury to personnel. All of these factors amply illustrate why it is essential that the entire string of shaped charges detonate in proper sequence. If they do not, the risk is significant both to personnel and equipment, and proper and safe execution of any remedial operations is very difficult.
One of the factors which increases the risk of failure is increasing temperature and pressure. Excessive pressure and temperature prevailing in a deep well act on the detonating cord to create problems which result in a high failure rate. Failures occur for a multitude of reasons. The detonator cord must connect with various detonators. In the presence of exceedingly high pressures and temperatures, the pressure may force fluid into the detonator and the protective boot which is attached to the detonator cord. This may cause a malfunction and thereby abort the detonation of the N shaped charges. Moreover, pressure may force the detonator cord, compressing the cord and explosive in the detonator housing, to alter the required position of the ignitor versus the ignition mix thereby impede proper firing or to cause poor firing.
With these problems in view, the present apparatus is a high pressure, high temperature detonator cord assembly which is particularly useful in high pressure high temperature wells. Moreover, the present apparatus can be installed with various detonator assemblies including a conventional bridge wire, exploding bridge wire, exploding foil initiator, percussion type initiator, and pressure actuated initiators. The apparatus incorporates a housing of sufficient wall thickness to withstand prevailing pressures. The appropriate primary explosive mix detonating cord and other components for operation are thus protected within the housing. More will be noted concerning this in detail hereinafter.